The possibility of ultraviolet (UV) light promoted exchange reaction (UVPER) between the primary alkanethiolate (AT) self-assembled monolayers (SAMs) and an azide-functionalized substituent (12-azido-1-dodecanethiol, C12N3), capable of click reaction with ethynyl-bearing species, is demonstrated. This reaction resulted in the mixed AT/C12N3 films, with the portion of C12N3 precisely controlled by selection of a suitable UV dose. As the primary matrix, either nonsubstituted or oligo(ethylene glycol) (OEG)-substituted AT SAMs were used, targeting mixed SAMs of chemical and biological significance. To demonstrate the flexibility of the approach, UV light with two different wavelengths (254 and 375 nm) was used, applied to the nonsubstituted and OEG-substituted AT SAMs, respectively. The surface density of the chemically active azide groups embedded in the nonreactive primary matrix could be varied according to the composition of the mixed SAMs, as demonstrated by the subsequent click reaction between these S...